Various products and materials are routinely irradiated to preserve or modify their characteristics. Among the processes employing irradiation are sterilization of medical devices, disinfection of consumer products, food irradiation for parasite and pathogen control, insect disinfestation and shelf-life extension, control of pathogens and toxins in drinking water, control of pathogens and toxins in liquid or solid waste, modification of characteristics of semiconductor devices, polymerization of monomers, grafting of monomers onto polymers, cross-linking or degradation of polymers, curing of composite materials, color enhancement of gemstones and other materials, and research on radiation effects on materials.
Biological materials that are prepared for human, veterinary, diagnostic and/or experimental use can contain unwanted and potentially dangerous biological contaminants or pathogens, such as viruses, bacteria, in both vegetative and spore states, (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, prions or similar agents responsible, alone or in combination, for TSEs and/or single-cell or multicellular parasites. Consequently, it is of utmost importance that any biological contaminant or pathogen in the biological material be inactivated before the product is used.
Ionizing radiation treatments such as gamma-irradiation, electron beam irradiation, and x-ray irradiation generate free radicals and other activated molecules that damage the biological components of contaminating bacteria, fungi, and viruses and thus ensures their inactivation. However, the biological materials may also be damaged by free radicals and activated molecules, which can harm the integrity of the material. In view of these issues, many new medical advances cannot be implemented because the sterilization industry is unable to provide a suitable procedure as part of the manufacturing process.
Issues involving sterilization exist in other areas of medical treatment as well, such as blood transfusions, blood factor replacement therapy, organ transplants and other forms of human therapy corrected or treated by intravenous, intramuscular or other forms of injection or introduction. Sterilization is also critical for the various biological materials that are prepared in media which contain various types of plasma and/or plasma derivatives or other biologic materials and which may contain harmful prions, bacteria, viruses and other biological contaminants or pathogens.
Irradiation processes are frequently characterized by the minimum absorbed dose required to achieve the desired effect and a maximum dose limit that is set on the basis of what the product can tolerate and still be functional. The dose distribution within a product depends on process load characteristics, irradiation conditions, and operating parameters. The operating parameters include electron energy and beam current, beam dispersion parameters and product material handling, including the control of a product's thermal profile. These parameters are particularly critical when the product is a radiation sensitive material.
U.S. Pat. No. 5,362,442 proposes a method for sterilizing products to remove biological contaminants such as viruses, bacteria, yeasts, molds, mycoplasmas and parasites. The method proposed requires providing the product in a form that contains less than 20% solids and subsequently irradiating the product with gamma irradiation over an extended period of time. The product is irradiated for a period of not less than 10 hours. The extended irradiation time in conjunction with the low level of solids in the product is said to substantially reduce the damage to the product. The method is said to be useful in sterilizing sensitive materials such as blood and blood components.
U.S. Pat. No. 6,187,572 proposes a method for inactivating viral and/or bacterial contamination in blood cellular matter, such as erythrocytes and platelets, or protein fractions. It is proposed that the cells or protein fractions are mixed with chemical sensitizers, frozen or freeze-dried, and irradiated with, for example, UV, visible, gamma or X-ray radiation while in the solid state.
U.S. Pat. No. 6,239,048 proposes a substrate such as a woven or nonwoven fabric bound with a light-activated dye alone or in combination with additional conventional antimicrobial agents. The proposed substrate is impregnated with a light-activated non-leachable dye said to have antimicrobial and/or antiviral characteristics that can be imparted to the substrate. Upon exposure to light, the dye is reported to generate singlet oxygen that is said to kill microorganisms and viruses.
U.S. Pat. No. 6,908,591 proposes methods for sterilizing biological materials to reduce the level of one or more active biological contaminants or pathogens, such as viruses, bacteria, yeasts, molds, fungi, prions or similar agents responsible, for TSEs and/or single or multicellular parasites. The methods proposed involve the use of flavonoid/flavonol stabilizers in sterilizing biological materials with irradiation.
W.O. Publication No. 98/31403 proposes methods of radiation-sterilizing a lyophilized collagen-based biomaterial and compositions of lyophilized collagen-based biomaterials.
Despite these advances in the art, there remains a need for methods of sterilizing radiation sensitive biological materials that are effective for reducing the level of active biological contaminants or pathogens without an adverse effect on the material itself.